Dual splined shaft

ABSTRACT

The present disclosure provides a lubricating system for a dual splined hollow shaft. A fluid dam is formed circumferentially within the hollow shaft to control the lubrication of the dual splines. The fluid dam includes a pair of sidewalls extending radially inward from the inner wall of the hollow shaft to a height defined by a top wall. A channel formed through the pair of sidewalls permits the movement of lubricant between splines of the hollow shaft. An egress port extends from the top wall of the dam through the outer wall of the hollow shaft to permit lubricant to exit the hollow shaft.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional PatentApplication 61/008,357, filed Dec. 20, 2007, and is incorporated hereinby reference.

GOVERNMENT RIGHTS

The present application was made with the United States governmentsupport under Contract No. N00019-04-C-0093 awarded by the U.S. Navy.The United States government has certain rights in the presentapplication.

FIELD OF THE INVENTION

The present invention relates to a dual splined shaft and moreparticularly to a lubrication system for the same.

BACKGROUND

Rotatable shafts can be coupled to gears or other shafts via a splineinterface. The spline interface must be lubricated appropriately toprevent wear or galling due to fretting, vibratory loading, or otherloading causing wear on the spline teeth. It is desirable to deliverenough lubrication to adequately protect the spline interface, butprevent excessive lubrication. Over lubrication requires additionalpumping and storage capacity in the lubricant system, which increasessystem cost, creates weight penalties, and causes additional space claimrequirements.

Dual splined shafts create additional challenges over single splineshafts. Because each spline must be lubricated, the splines must eitherhave separate lubrication delivery systems or a single system must beable to deliver adequate lubrication to both ends of the shaft. Duallubrication systems are expensive due to the redundancy and singlesystems tend to either over or under lubricate at least one of thesplines.

One method of single source lubrication is to provide an opening in thewall of a partially hollow shaft and spray lubricating fluid toward theopening. One drawback to this type of system is that a significantamount of the lubrication will not pass through the opening because theshaft is rotating. The bigger the opening the more likely the lubricantwill enter the hollow shaft, but the large opening makes it more likelythat the lubricant will exit back out of the hollow shaft before movingto lubricate either of the splines. Furthermore the size of the openingis limited by the geometry of the shaft and the associated mechanicalstress induced in a load bearing wall because of the large opening. Ifthe opening is too small more lubricant is “wasted” as it hits the outerwall of the shaft and fails to enter through the opening as the shaftrotates. The present inventions provide novel and non-obvious,innovation needed in this field of technology.

SUMMARY

The present invention includes an apparatus and method for lubricating adual splined shaft. Further embodiments, forms, features, aspects,benefits, and advantages shall become apparent from the description andfigures provided herewith.

BRIEF DESCRIPTION OF THE DRAWINGS

The description herein makes reference to the accompanying drawingswherein like reference numerals refer to like features throughout theseveral views, and wherein:

FIG. 1 is schematic top view of a gear box having a plurality of splinedshafts projecting therefrom;

FIG. 2 is a cutaway of the gear box of FIG. 1 showing a cross section ofa shaft having dual spline couplings;

FIG. 3 is an enlarged perspective view of one end of the dual splinedshaft with an input/output shaft engaged therewith and a lubricationnozzle spraying lubrication under a spline coupling; and

FIG. 4 is a cross sectional view of the splined coupling shown in FIG.3.

DETAILED DESCRIPTION

For purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated device, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

The inventions disclosed herein includes means for lubricating a dualsplined shaft i.e. a shaft having splines on opposing ends thereof. Thedual splined shaft can be coupled to input/output shafts or otherrotating components having mating spline connections. While thedisclosed embodiment depicts female couplings or internal splinedcouplings on the dual splined shaft, it should be readily understood byone skilled in the art that male couplings or external splined couplingscould be implemented on the dual splined shaft. Furthermore the dualsplined shaft may have a combination of both a male spline and a femalespline. The lubrication system including any nozzles and spray geometrymay be modified to utilize a dual splined shaft with a male couplingwithout departing from the teachings of the present invention.

The dual splined shaft of the present invention is substantially hollowto permit lubrication fluid or lubricant to move freely between opposingends of the shaft. One aspect provides for a shaft design with desiredlubrication at the opposing coupling ends while minimizing the volumeand dwell time of the lubricant within the hollow shaft. If the volumeor dwell time of the lubricant in the dual splined shaft is more thanthe required amount then the lubrication system will not be optimized.This non-optimization requires larger volume oil sumps and highercapacity pumps which in turn leads to space claim and weightpenalties—all which translates into higher system costs. The presentinvention ensures that both splines are adequately lubricated and thatlubricant is expelled at a desired rate to prevent excess lubricant frombuilding up within the hollow shaft.

For purposes of this disclosure lubricating fluid can include any commonor non-common lubricant known to those skilled in the art. In oneexample the fluid can be a carbon based mineral oil, in another examplethe fluid can be a synthetically produced lubricant, and in otherexamples the fluid can combinations of natural made lubricants and manmade lubricants.

Referring to FIG. 1, a schematic representation of a gear housing 10having a plurality of shafts 12, 13, and 15 extending therefrom isillustrated. Each of the shafts 12,13,15 can include a spline coupling14 on the ends thereof. While a gear housing is illustrated in theexample embodiment, it should be understood that the present inventioncan be utilized with any shafting or gear configuration in which itwould be advantageous to use a dual splined shaft. Material selectionfor the shafts, gears, splines and other rotating components disclosedherein are generally known to those skilled in the art. Materials mayinclude, but are not limited to metals, ceramics, composites, plasticsand any combination thereof.

Referring now to FIG. 2, the gear housing 10 can have a dual splinedshaft 16 operable to transmit rotation or torque between the pair ofsplined shafts 12, 13. The splined shafts 12, 13 can be input shafts,output shafts or any other rotating component such as gears and thelike. The dual splined shaft 16 includes a first end 18 having a firstsplined coupling 20 and a second end 22 having a second splined coupling24. The dual splined shaft 16 has a substantially hollow core 26 topermit lubricating fluid to internally travel along the length of theshaft 16 between the first and second spline couplings 20, 24.

The shaft 16 includes a fluid dam 28 protruding radially inward from aninner wall 30. The fluid dam 28 can extend circumferentially around theentire inner wall 30. The fluid dam 28 includes a pair of sidewalls 27,29 extending radially inward toward a top wall 36. At least one channel32 extends through the sidewalls 27, 29 and can be positioned at asufficient depth such that lubricating fluid can flow past the fluid dam28 through the at least one channel 32. In one form the depth of thechannel 32 is substantially flush with the inner wall 30 of the hollowshaft 16. At least one fluid egress port 34 extends from the top wall 36of the dam 28 through an outer wall 38 of the shaft 16 to permitlubricating fluid to egress out of the dual splined shaft 16.

First and second seal assemblies 42, 43 are positioned adjacent thefirst and second ends 18, 22, respectively of the shaft 16. The sealassemblies 42, 43 restrict lubrication fluid from exiting the dualsplined shaft 16 through the ends thereof. The seal assemblies 42, 43can include a fluid seal 45 such as an o-ring or the like to seal aninterface portion of the inner wall 30 of the dual splined shaft 16 withthe coupled shafts 12, 13. The seal assemblies 42, 43 are preferably asingle continuous component mounted on the coupled shafts 12, 13 priorto installation, but alternatively embodiments can include multi-piececonstruction that can be installed after the shafts 12 and 13 arecoupled with the dual splined shaft 16 as one skilled in the art wouldreadily understand. The first seal assembly 42 includes at least oneingress port 40 for permitting lubricating fluid to enter into the shaft16 and lubricate the splined couplings 20, 24. In one non-limitingembodiment the ingress port 40 includes a plurality of elongated slottedapertures formed under the O-ring or seal portion 45 of the sealassembly 42 (best seen in FIG. 3). Because of the centripetalacceleration force due to high speed rotation of the shaft 16, thelubricating fluid will move radially outward toward the inner wall 30 ofthe shaft 16 and will be restricted from flowing past the seals 45 ofthe seal assemblies 42, 43.

Referring now to FIGS. 3 and 4, the first end 18 of the shaft 16 isillustrated with a nozzle 48 directing a spray 49 of lubricating fluidtoward the ingress port 40. The nozzle 48 can spray lubricating fluidsubstantially in the direction along the axis of rotation X. Thelubricating fluid enters through the ingress ports 40 as the dualsplined shaft 16 is rotating. The port 40 permits lubricating fluid topass under the seal 45 of the seal assembly 42 and into the splinecoupling 20. The seal 45 of the seal assembly 42 substantially restrictsthe lubricating fluid from escaping back out through the first end 18 ofthe shaft 16. The lubricating fluid then flows through the splinedcoupling 20 connecting the coupled shafts 16 and 12 to one another.After the lubricating fluid passes through and lubricates the splinedcoupling 20, the lubricating fluid traverses into the hollow portion ofthe shaft 16.

As described above, because the dual splined shaft 16 rotates at arelatively high speed the lubricating fluid in the hollow portion willmove toward the surface of the inner wall 30 (best seen in FIG. 2). Asthe lubricating fluid continues to flow into the hollow portion of theshaft, the fluid will pass across the dam 28 via the at least onechannel 32. When the hollow shaft 16 is partially filled withlubricating fluid, the fluid will move to the second end 22 andlubricate the second splined coupling 24. The lubricating fluid isprevented from escaping past the coupling 24 at the second end 22because the seal 45 of the second seal assembly 43 (see FIG. 2) forms afluid tight connection between dual splined shaft 16 and the coupledshaft 13. The lubricating fluid will continue to build up along theinner wall 30 of the rotating shaft until it rises above the top wall 36of the dam 28. After the lubricating fluid reaches the height of the topwall 36, any additional fluid entering the hollow shaft 16 will causethe lubricating fluid to exit through the egress ports 34 and flow backto a fluid sump (not shown). During operation, the height of the dam 28will control the amount of lubricating fluid retained in the hollowshaft 16 and the number and size of the egress ports 34 will control howfast the lubricating fluid is expelled from the hollow shaft 16. Atshutdown, lubricating fluid can egress through the inlet ports 40because the centripetal force has been removed. In this manner bothspline couplings 20, 24 of the dual splined shaft 16 will be adequatelylubricated and the quantity of lubricating fluid disposed within thehollow shaft 16 is controlled by the dam 28 during operation.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment(s), but on the contrary, is intended to covervarious modifications and equivalent arrangements included within thespirit and scope of the appended claims, which scope is to be accordedthe broadest interpretation so as to encompass all such modificationsand equivalent structures as permitted under the law. Furthermore itshould be understood that while the use of the word preferable,preferably, or preferred in the description above indicates that featureso described may be more desirable, it nonetheless may not be necessaryand any embodiment lacking the same may be contemplated as within thescope of the invention, that scope being defined by the claims thatfollow. In reading the claims it is intended that when words such as “a,an,” “at least one” and “at least a portion” are used, there is nointention to limit the claim to only one item unless specifically statedto the contrary in the claim. Further, when the language “at least aportion” and/or “a portion” is used the item may include a portionand/or the entire item unless specifically stated to the contrary.

1. A system for lubricating a dual splined shaft comprising: a hollowrotatable shaft having an inner wall and an outer wall and first andsecond splines associated with opposing ends thereof; first and secondcomponents connected to the hollow shaft via a spline coupling; and afirst fluid seal assembly positioned at an interface between the firstcomponent and the hollow shaft, the first fluid seal assembly includingat least one fluid passageway for transporting lubricating fluid to thesplined couplings.
 2. The system of claim 1 further comprising: a secondfluid seal for sealing an interface between the second component and theopposing end of the hollow shaft.
 3. The system of claim 1 furthercomprising: a fluid dam formed within the hollow shaft, the fluid damhaving a pair of sidewalls extending radially inward from the inner wallof the hollow shaft to a height defined by a top wall formed between thesidewalls.
 4. The system of claim 3, wherein the fluid dam extendscircumferentially around the entire inner wall of the hollow shaft. 5.The system of claim 3, wherein the fluid dam comprises: at least onechannel formed through the pair of sidewalls; and at lease one egressport extending from the top wall of the dam through the outer wall ofthe hollow shaft.
 6. The system of claim 5, wherein the bottom of thechannel is substantially flush with the inner wall of the hollow shaft.7. The system of claim 5, wherein the lubrication fluid flows throughthe fluid passageway of the seal assembly, passes through and lubricatesthe first splined coupling, enters into the hollow shaft and traversesthough the at least one channel to the opposing end and lubricates thesecond splined coupling.
 8. The apparatus of claim 5, wherein thelubrication fluid fills the hollow shaft to a height of the top wall ofthe dam and egresses from the hollow shaft through the egress port. 9.The system of claim 1 further comprising: a lubrication system includinga pump and a nozzle for supplying lubrication fluid to the dual splinedhollow shaft through the at least one fluid passageway of the first sealassembly.
 10. The apparatus of claim 9, wherein the primary direction ofthe lubricating fluid spray from the nozzle is substantially along theaxis of rotation of the hollow shaft.
 11. A method of lubricating a pairof splines of a hollow dual splined shaft comprising the steps of:delivering lubricant to a splined shaft through a passageway in a sealassembly proximate one end of the shaft; directing the lubricant througha first splined coupling associated with the shaft; flowing lubricantinto a first end of the hollow shaft; traversing the lubricant past adam in the shaft; moving the lubricant to a second end of the hollowshaft; lubricating a second splined coupling; and ejecting lubricatingfluid from the hollow shaft.
 12. The method of claim 11, wherein thetraversing step includes flowing the lubrication fluid through a channelformed in the dam.
 13. The method of claim 11, wherein the ejecting stepincludes filling the hollow shaft with lubrication fluid up to theheight of the dam; and flowing lubrication through the outlet portformed at a top of the dam.
 14. The method of claim 11 furthercomprising sealing the splined couplings at either end to restrictlubrication fluid from egressing from the hollow shaft through theopposing ends thereof.
 15. The method of claim 11, wherein thedelivering step includes spraying lubricating fluid in a directionsubstantially parallel to the axis of rotation of the dual splinedshaft.
 16. An apparatus comprising: a hollow rotatable shaft having aninner wall and an outer wall; first and second splines associated withopposing ends of the shaft; a fluid dam formed within the hollow shaft,the fluid dam having a pair of sidewalls extending radially inward fromthe inner wall of the hollow shaft to a height defined by a top wallconnecting the sidewalls; at least one channel formed through the pairof sidewalls; and at lease one egress port extending from the top wallof the dam through the outer wall of the hollow shaft.
 17. The apparatusof claim 16, wherein the bottom of the channel is substantially flushwith the inner wall of the hollow shaft.
 18. The apparatus of claim 16further comprising first and second splined components connected to thesplines of the hollow shaft.
 19. The apparatus of claim 18, wherein thecomponents are one of a gear and a shaft.
 20. The apparatus of claim 18further comprising: a pair of seal assemblies operably connected betweenthe splined components and the hollow shaft.
 21. The apparatus of claim20, wherein the pair of seal assemblies restrict lubricating fluid fromexiting the hollow shaft proximate the ends thereof.
 22. The apparatusof claim 20, wherein one seal assembly includes at least one inlet portfluidically connected to the hollow shaft via one of the splines.